Optical Diode Reverses Time, Making Photo-Based IC Possible

Researchers at Washington University in St. Louis have built what could become a critical component for microprocessor circuits that crunch data using light rather than electricity. The group developed a system of optical resonators that intensifies light traveling in one direction and weakens it to virtually nothing in the other -- and shrank the whole thing down so it's small enough to fit on a silicon chip.

The component does the same job that a simple diode would in an electrical system. It does so using a twisting concept of quantum mechanics that not only keeps light flowing in one direction and not the other, but appears to let more energy out of the device than went in. Inside a doughnut-shaped component, two microresonators reflect light back and forth. One tends to lose energy, while the other increases it. When the loss equals the gain at a specific wavelength, the system goes through a phase change in which the roles of the resonators are reversed, “their temporal relationships reverse, loss becomes gain and gain becomes loss," according to a paper describing the technique that was published in the April 6 issue of Nature Physics.

In an optical diode, the light input in one direction is transmitted, while the light input in the opposite direction is blocked. The new optical diode, designed by the university researchers, is made from parity time symmetric microresonators in which the loss of one of the resonators is balanced by the gains in the other. (Source: Washington University)

The result could make it practical to build integrated computing circuits that use beams of light that travel along channels far narrower than would ever be possible using wire and electricity, and at far lower energy levels. The process could still support standard semiconductor circuitry designs.

"At present, we built our optical diodes from silica, which has very little material loss at the telecommunication wavelength. The concept can be extended to resonators made from other materials to enable easy CMOS compatibility," according to Bo Peng, a graduate student in Yang’s group and lead author of the paper.

Metaphorically, the device works in a way similar to the Whispering Gallery in St. Paul's Cathedral, in which oddities of acoustics make quiet noises audible at one end of the side of the gallery when they are nearly inaudible to those standing nearby.

Kudos to the team for the revolutionary discovery!! Don't really understand how it works as I lost touch with optics/quantum physics. I guess, the work is going on to have Optical PCBs and Optical ICs, so I guess life would be easier as the products made out of optical ICs and optical PCBs would be much less prone to EMI/EMC issues? While feeling happy about that, at the same time a thought that occurs...it would be a different world for the engineers...how one would probe signals for debugging? A new set of tools would evolve and may be a new set of standards too to comply with?

Optical wavelengths and electroonic signals all work the same way. Different materials change the rate at which each wavelength propagates through the substance. It is not time reversal, it is just index of refraction.

I do agree that the optical frequencies are probably our next venue of exploitation, but the real payoff comes from the X-ray frequencies and above.

A micro miniature optical diode that is compatible with semconductor manufacturing processes could indeed open up many exciting new possibilities -- but is it really non-causal? Your headline seems to suggest that the output appears before the input -- or did you mean something else by "time reversal?"